This invention relates to energy intensive chemical reactions at surfaces, and, more particularly, to accomplishing chemical reactions at surfaces when both a reactant and energy are externally supplied to accomplish the reaction.
Various types of chemical reactions occur or are produced at surfaces. In some reactions, such as most catalysis reactions and the deposition of a reaction product film wherein the reactants are supplied from an external source, the surface provides a site for the reaction to occur but does not itself provide a chemical reactant. In others, such as the etching of a surface or the growth of a film of a reaction product formed by a reaction involving the atoms or molecules at the surface, the surface itself enters into the reaction by supplying a reactant.
Many surface reactions are, or could be, of great commercial significance. Catalysis reactions are widely used to produce chemical products. The chemical etching of films, a chemical process wherein a portion of the film is reacted and removed, is a central feature of microelectronic fabrication technology. Reactive deposition of films onto a surface, as in chemical vapor deposition, permits production of special types of films for electronic and optical applications that cannot be produced otherwise.
Many of the reactions that occur at surfaces require the input of energy to overcome a reaction energy barrier. Most chemical reactions are accelerated when the reactants are energized, and faster chemical reactions improve the economics of using the surface reactions. The most common approach to providing energy is to heat the surface through the underlying substrate, thereby energizing the reactants at the surface. When applied in the context of deposition of a film of a reaction product, this approach has the drawback of also heating the previously deposited layers. This heating of the prior layers can cause an undesirable interdiffusion of the layers, where different layers have been deposited on top of each other.
Another approach to providing energy to the reaction occurring at the surface is to direct energy at the surface, as with a laser beam or ultraviolet light. This approach has been successful in some applications, but requires that the incident beam be properly tuned and directed to couple its energy to that of the reactants. It is desirable to make the directed beam as intense as possible to transfer a high energy level, but intensity is limited by the transfer of heat to the surface. Some of the heat can be removed by cooling the substrate, but unintended heating and even melting of the surface layers is a limitation on the power that can be introduced into the surface reaction. Another approach to energizing the surface is to create a plasma at the surface, but the field of the plasma often limits the ability to bring further reactants to the surface, is difficult to control as to the amount of energy input, and may have undesirable side effects on the surface.
Thus, while the use of surface reactions is well established and widely used commercially, and the need to provide energy to at least some types of reactions is recognized, there continue to be difficulties in introducing both reactants and energy to the surface as the reaction proceeds. There is a need for a technique for providing both reactants and energy to the surface, in a controllable manner. The present invention fulfills this need, and further provides related advantages.